Abstract
This thesis deals with the design and development of a process for the conversion of wet biomasses, primarily to H2. Wet biomasses contain over 80% moisture, such as bio-wastes and wastewaters produced in the food and agro-industries. In order to overcome the energy-intensive drying step for traditional biomass conversion technologies, a newer route for conversion involves the use of water as a reaction medium. Such processes are hydrothermal in nature. The process under consideration in this thesis is a two-step catalytic process for hydrothermal gasification with simultaneous reduction of the organic content of the residual water phase.
The first part of the thesis (Chapters 2 and 3) includes studies focussed on obtaining a more fundamental understanding of the two main catalytic processes under consideration: stabilisation and gasification. Stabilisation, described in Chapter 2, was successfully applied to convert highly reactive aqueous carbohydrates to more stable molecules that would subsequently minimise, if not eliminate, coke production upon further processing. In Chapter 3, the hydrothermal gasification of sorbitol was studied using a 5 wt % Pt on γ-Al2O3 catalyst, with an without N2 as a sweep gas. The complex reaction mechanisms were described through a path-lumped kinetic scheme. The reactor model was used to demonstrate the feasibility of the process on an industrial scale. The second part of this thesis (Chapters 4 and 5) includes work focussed on process development with an aim to identify whether the process is ready for implementation on a larger, industrial scale. In Chapter 4, a sequential combination of the studied gasification catalysts (Pt and Ru) was found to provide a two-fold advantage to the hydrothermal gasification process, through the optimal production of H2, at complete carbon to gas conversions. In Chapter 5, a process development and economic analysis was conducted. An energy balance demonstrated that the process an overall energy efficiency of 65 %. The rest of the energy produced (~ 35 %) was used to meet the process demands of electricity, steam and fired heat. The price of H2 obtained was comparable to H2 prices obtained from other renewable technologies.
The first part of the thesis (Chapters 2 and 3) includes studies focussed on obtaining a more fundamental understanding of the two main catalytic processes under consideration: stabilisation and gasification. Stabilisation, described in Chapter 2, was successfully applied to convert highly reactive aqueous carbohydrates to more stable molecules that would subsequently minimise, if not eliminate, coke production upon further processing. In Chapter 3, the hydrothermal gasification of sorbitol was studied using a 5 wt % Pt on γ-Al2O3 catalyst, with an without N2 as a sweep gas. The complex reaction mechanisms were described through a path-lumped kinetic scheme. The reactor model was used to demonstrate the feasibility of the process on an industrial scale. The second part of this thesis (Chapters 4 and 5) includes work focussed on process development with an aim to identify whether the process is ready for implementation on a larger, industrial scale. In Chapter 4, a sequential combination of the studied gasification catalysts (Pt and Ru) was found to provide a two-fold advantage to the hydrothermal gasification process, through the optimal production of H2, at complete carbon to gas conversions. In Chapter 5, a process development and economic analysis was conducted. An energy balance demonstrated that the process an overall energy efficiency of 65 %. The rest of the energy produced (~ 35 %) was used to meet the process demands of electricity, steam and fired heat. The price of H2 obtained was comparable to H2 prices obtained from other renewable technologies.
| Original language | English |
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| Award date | 12 Jul 2019 |
| Place of Publication | Enschede |
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| Print ISBNs | 978-90-365-4800-7 |
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| Publication status | Published - 12 Jul 2019 |